Display systems of various types are known. Many such systems utilize a display panel that must be backlit with a large area backlight in order for the user to perceive the image generated by the display panel. Such systems are popular in display screens for laptop computers, mobile communication devices, and similar electronic devices. The backlight, which may include one or more diffusing film, reflecting film, prismatic film, light guide, and light source, for example, emits white light over an output area that is substantially the same size as the display panel. The display panel, e.g., a liquid crystal (LC) display panel, has a matrix of individually addressable elements (referred to as picture elements or “pixels”) that can be controlled via an electronic control unit to transmit red, green, and/or blue light from each pixel. In many cases, the area of a given pixel in plan view is subdivided into three smaller independently addressable areas—one to regulate red light, one to regulate green light, and one to regulate blue light—and these are referred to as subpixels. In some display technologies, however, the subpixels are coextensive with the associated pixel, i.e., they do not have a smaller area than the associated pixel.
Display systems that operate based on reflected light, rather than transmitted light, are less common than transmissive-type displays. This may be due in part to complications relating to the choice of the external light source, its placement relative to the display panel and the viewer, and challenges in providing adequate brightness. In some cases, ambient daylight may be relied upon as the source of external light. In other cases, an electrically powered light source may be used, and mounted in a specific location designed to provide optimum viewing.
Metal halide lamps have become increasingly popular in commercial, residential, and industrial lighting applications. For example, metal halide lamps are used to illuminate sports stadiums and other athletic facilities. One reason for the popularity of these lamps is their relatively efficient operation relative to incandescent, fluorescent, and mercury vapor lamps, and their ability to provide white light of suitable color temperature and color rendering index (CRI) for many applications.